Implantable drug infusion pumps have been in existance for many years. They are used primarily for the long-term infusion of drugs in patients having chronic diseases such as diabetes, cancer and the like. In general, such pumps comprise a pressurized drug source which can be refilled while the device is implanted. A flow regulator regulates the flow of fluid from the source to an outlet catheter which delivers the drug from the flow regulator to a specific infusion site in the body; see, for example, U.S. Pat. No. 4,978,338 and the references cited therein.
Implantable pumps also exist which contain means whereby a drug or other fluid can be administered directly to the patient via the pump's outlet catheter, bypassing the pump's pressurized source; see for example, U.S. Pat. No. 4,496,343. Such a feature is considered essential in order to make the pump a versatile therapeutic tool. Indeed, there are many situations in which supplemental medication must be administered to a patient in addition to the drug being slowly infused into the patient from the pump's drug source. For example, fluids which are opaque to x-rays are sometimes injected through the pump's outlet catheter in order to verify that the pump is indeed infusing those organs or parts of the body which have been targeted for the prescribed drug therapy. As another example, if the pump's outlet catheter is positioned in a blood vessel, there is the potential that the catheter may become occluded by blood clots or thrombus. In such a situation, fluid flow through the catheter can be restored if an agent which can dissolve clots can be injected directly into the lumen of the outlet catheter.
FIG. 1 illustrates a typical prior pump with a bolus capability. It includes a housing 10 having an internal chamber 12 containing a collapsible fluid reservoir 14, e.g., a bellows capsule. Extending down into the top of housing 10 is an inlet port 16 which is connected to the interior of the reservoir 14 by an inlet conduit 18 in housing 10. The mouth of the inlet port 16 is closed by a self-sealing, needle-penetrable septum 20. The septum effectively isolates the port segment 16a below the septum, the conduit 18 and the interior of reservoir 14 from the atmosphere. The segment 16a thus forms a refill chamber in housing 10.
Also formed in housing 10 is an outlet passage 22 which leads from the interior of reservoir 14 to a fluid flow regulator 24, e.g., a capillary tube. The outlet from regulator 24 extends to one arm of a T-shaped outlet conduit 26 formed in housing 10, the leg of the T being connected to a flexible outlet catheter 28. When the pump is implanted, the distal end of catheter 28 is positioned at a selected infusion site in the body.
The other arm of outlet conduit 26 leads to a bolus inlet port 32 extending down into housing 10. The mouth of port 32 is closed by a self-sealing septum 34 similar to septum 20 thereby isolating the lower end segment 32a of passage 32 from the atmosphere. Thus that segment constitutes a bolus chamber in housing 10.
The chamber 12 of the pump is normally filled with a fluid such as triclorofluoromethane which vaporizes at physiological temperatures. Thus, when the pump is implanted in the body, the fluid in chamber 12 will vaporize and exert a positive pressure on reservoir 14 which tends to collapse the reservoir so that an infusate in the reservoir will be forced out of the reservoir through the outlet passage 22, regulator 24 and conduit 26 to the outlet catheter 28. Septum 34 prevents infusate in reservoir 14 from escaping through bolus port 32. As described in the above patents, infusate will continue to flow from reservoir 14 to the patient in a controlled manner until the contents of reservoir 14 are depleted.
The methods used to refill reservoir 14 or to bolus fluid directly to catheter 28 via the bolus chamber 32a are very similar. In general, a hollow needle is connected to a syringe containing the fluid to be injected. The needle is then inserted through the patient's skin above the implanted pump and through one of the septa 20 and 34 at the top of the pump. The fluid is injected through the needle and into the chamber 16a or 32a below the corresponding septum. The conduit 18 or 26 within the pump conducts the fluid either to the reservoir 14 or directly to catheter 28 depending upon which septum 20 or 34 has been penetrated.
Thus, if the needle penetrates septum 20 the delivered drug flows into reservoir 14. In that event, as described in the above patents, the refilling of the reservoir also exerts positive pressure on the fluid inside chamber 12 so that that fluid condenses thereby, in effect, recharging the pump. On the other hand, if the needle is inserted through septum 24, the delivered drug is bolused to outlet catheter 28, thereby bypassing reservoir 14 and flow regulator 24.
Normally, it is up to the healthcare professional to access the correct septum for the type of procedure to be performed, i.e., either reservoir refill or bolus to the outlet catheter. As might be expected, accidents have occurred in the past because the wrong septum was accessed inadvertently. For example, the drug which was intended to be injected into the pump's reservoir 14 to refill the reservoir was injected instead directly into the patient via the outlet catheter 28. Obviously such accidents can be dangerous to the patient. For example, in some cases, the reservoir 14 of a given pump may be filled with as much as a four week's supply of drug. Depending upon the drug used, such a four week's supply may be harmful if administered to the patient all at once by injection through the septum 34 instead of the septum 20. It would be desirable, therefore, if there existed an implantable pump having dual inlet ports which prevented such misdelivery of drugs to the pump.